Both of these boards will float WAY better than the Slayblade (great deck for many things - powder not really one of them). Magic even more floaty than the T. Rice and much more playful/lively (but also more squirrelly at speed - basically a much more rockered board than the T. Rice), so the 157 might work for you.
Note that for the T. Rice the trade-off between the 157 and 161.5 is going to be greater than for the 157 and 161 Magic - not only are you adding 3.5cm of contact length (vs. 3cm on the Magic) and a pointy nose/tail, you are also going to a slightly larger sidecut radius 8.2m to 8.4m, while the Magic is 7m at all sizes).
As a result the difference between the different sizes will be more marked - the 161.5 will gain quite a bit of powder capability, but is also more if a bomber board than a playful deck. In contrast, the Magic just 'sizes up' without much change in character.